The invention relates to extruders and like machines wherein a stream of plasticized synthetic plastic material is caused to continuously flow into one or more mold cavities. More particularly, the invention relates to apparatus for filtering the flow or stream of plasticized synthetic plastic material in such machines.
German Auslegeschrift No. 18 00 169 discloses a filtering apparatus which can be used in an extruding or injection molding machine (hereinafter called extruder for short). The apparatus is constructed and assembled in such a way that it allows for replacement of a contaminated, damaged, clogged and/or otherwise affected filter without interrupting the flow of plasticized material from the inlet to the outlet of the housing for the filter and without permitting a bubble of air to interfere with predictable flow of plasticized material to the outlet. A drawback of the apparatus which is disclosed in this German publication is that it constitutes a bottleneck between the unit or units which are disposed upstream and the unit or units which are disposed downstream of the filtering station. The development of extruders has progressed to such an extent that the units upstream and downstream of the filtering station can form and process plasticized synthetic plastic material in quantities greatly exceeding those which can be filtered per unit of time in a conventional filtering apparatus.
Attempts to prevent the development of bottlenecks in the region of the filtering apparatus involve the utilization of large filters including huge sieves with correspondingly enlarged carriers for the sieves. This, in turn, creates problems in connection with the shifting of such carriers to and from the positions in which the sieves are accessible and to and from the positions in which the sieves are ready to intercept impurities and/or other foreign matter in the stream of plasticized synthetic plastic material. Moreover, the cost of large filters and outsized carriers for such filters is extremely high so that the increased cost does not warrant the utilization of such filters and carriers in existing extruders.